More caterpillar problems discovered
In the summer of 2010, the Idaho State Department of Lands (IDL), the Washington State Department of Natural Resources (DNR), and the U.S. Forest Service detected new areas with defoliation by a caterpillar called the Douglas-fir tussock moth in Kootenai and Benewah counties in Idaho, and Spokane County in Washington.
Through aerial surveys, approximately 8,500 acres affected in northern Idaho and close to 570 acres with defoliation in eastern Spokane County were mapped.
The damage primarily affects grand fir and Douglas-fir. Defoliation damage has been moderate, affecting the top third of the tree crowns. This damage can reduce growth, cause top-kill and may predispose some trees to attack by bark beetles. Recreation can also be affected in areas with tussock moth present because the caterpillars’ hairs are a skin irritant to many people.
Areas with defoliation in Idaho include the Signal Point area, south of Post Falls; near Twin Lakes, northeast of Rathdrum; and in the vicinity of Plummer. George Bacon, Director of Idaho Department of Lands, expressed that IDL staff will continue to monitor the outbreak and will be communicating with landowners in the coming months who own more than five acres in the affected areas. Specific areas affected in Spokane County are Mica Peak, Tekoa Mountain, Gelbert Mountain and Liberty Lake.
Ground surveys for egg masses indicate that defoliation in these areas may expand and increase in severity in the summer of 2011. Outbreaks typically collapse within two to four years due to a buildup of natural enemies, such as a virus and parasites. Most likely, 2010 was the second year of this outbreak.
The caterpillar life-stage of the Douglas-fir tussock moth prefers to eat the needles of grand fir and Douglas-fir trees. The Douglas-fir tussock moth is an insect, native to the Inland Northwest, with populations that run in cycles, dropping for a period of years between major outbreaks. The last outbreak in the northern Idaho-Washington State border area was from 2000-2002. The last outbreak in Washington occurred in Okanogan County from 2008 to 2010, leaving more than 3,500 acres defoliated at its peak in 2009.
IDL and DNR are asking forest and woodlot property owners in these areas to be on the lookout for signs and symptoms of Douglas-fir tussock moth. Tussock moth cocoons and egg masses can be found on the underside of tree branches and structures such as building overhangs and fences. Defoliation damage looks like reddish half-chewed needles and tends to be worst in the tops of trees. To report tussock moth damage or for more information, please contact your state’s Forest Entomologist: Tom Eckberg (Idaho Dept. of Lands) or Glenn Kohler (Washington DNR) .
A combination of careful tree thinning and, where appropriate, the application of biological control chemicals can reduce tree damage and may prevent an outbreak’s spread. To evaluate management options, IDL and DNR can assist forest and woodlot property owners in the affected area who observe Douglas-fir tussock moth egg masses or tree damage.
Detailed information on how to recognize Douglas-fir tussock moth damage, maps and images are available at the IDL and DNR websites:
Idaho:
http://www.idl.idaho.gov/bureau/ForestAssist/forest_health/foresthealth_index.html